Logic simulation is a widely used method of computing the operational performance of theoretical logic circuits for the purpose of verifying a desired circuit operation and eliminating design errors. By using logic simulation, a circuit designer can test a theoretical circuit design by simulating its performance on a computer, thereby saving the cost and time required to build, test and correct an actual physical system. Prior art logic circuit simulators produce output data, either in the form of tabular computer listings or as a static graphical display. While both output formats allow a circuit designer to analyze the operation of a logic circuit, in practice, both computer listings and static displays are very limited in their ability to convey the effects of complex time-varying signals upon the simulated logic circuit being tested.
Complex time-varying signals are common in many applications such as navigation, radar, electronic countermeasure devices and communication systems. The time variations within such applications are often the result of either asynchronous signals from separate sources, pulse trains whose rates vary with time, or objects such as satellites and aircraft that produce relative motion between a signal transmitter and receiver. Regardless of the actual application of a logic circuit that utilizes time varying signals, once the logic circuit is built, it is usually tested using an oscilloscope or like device that produces a realtime visual display of the time varying signals. As will be recognized by a person skilled in the art, a great deal of information concerning the correct operation of a logic circuit is derived from observing the signal waveforms on the oscilloscope as they vary in real time.
When logic circuits that utilize time-varying signals are designed, the use of a real time oscilloscope is not an option until after the circuit is built. In order to test the logic circuit prior to its construction, a logic circuit simulation system must be used. Prior art logic circuit simulation systems produce static outputs. As such, the use of a prior art logic circuit simulation system cannot effectively convey, to a circuit designer, the effects of a time varying test signal on the logic circuit being tested, and a great amount of analytical information concerning the circuit design is lost. Furthermore, as logic circuits become more complex, static data becomes increasingly difficult to interpret. Thus, it has become increasingly difficult to detect design errors, within theoretical logic circuits, prior to the expense and labor of actually creating the complex circuit and testing it with a traditional oscilloscope.
It is therefore a primary objective of the present invention to set forth an apparatus and method whereby static prior art simulation data is converted into real-time video images so that a time-varying nature of a test signal can be visualized as a waveform on a video display. The present invention, therefore, facilitates the oscilloscope-like analysis of a theoretical logic circuit by dynamically displaying the operational performance characteristics of the logic circuit on a screen prior to the physical construction of the circuit being tested.